Now scientists are investigating how events in a mineral layer at the core-mantle boundary, 1,615 miles (2,600 kilometers) deep, similarly affect the planet's spin.

"The length of a day is changing due to the interaction between the mantle and the core in the very deep Earth," said study co-author Kei Hirose, a geoscientist at the Tokyo Institute of Technology in Japan.

"This is basically because the bottom of the mantle has very high electrical conductivity."